Paper multi-feed detection apparatus and paper multi-feed detection method

ABSTRACT

A paper multi-feed detection apparatus and a paper multi-feed detection method are provided for preventing the detection capability from being deteriorated by a noise factor and improving the detection precision even where an area around the feeding path has no extra space in terms of the shape and there are many noise-generating factors because of a demand for a smaller size of the device. An ultrasonic transmission opening formed in one of two feeding guide plates is large so as to discharge outside a reflected wave which returns through the ultrasonic transmission opening, and an ultrasonic receiving opening formed in the other feeding guide plate is smaller than a receiving face area of a receiver for receiving the ultrasonic wave.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a paper multi-feed detection apparatus applicable to office equipment such as, for example, copiers and scanners, and more specifically to a paper multi-feed detection apparatus and a paper multi-feed detection method for accurately detecting that sheets of paper such as blank or printed forms, banknotes, gift certificates, book coupons, checks, cards and the like are fed in an overlapped state.

2. Description of the Prior Art

Recently, as an apparatus for detecting multi-feed of sheets of paper which easily tend to be fed in an overlapped state, for example, sheets of thin paper or the like, a paper multi-feed detection apparatus using an ultrasonic sensor is known. When such an ultrasonic sensor is used to detect sheets of paper, the following detection capabilities unique to the ultrasonic sensor are provided.

(1) Since detection is performed without any contact with the paper sheets, feeding of the paper sheets is not disturbed.

(2) Since detection can be performed regardless of the thickness of the paper sheet, multi-feed can be detected even where paper sheets having different thicknesses are present.

(3) Since detection can be performed regardless of the color of the paper sheet, no adjustment is necessary for different colors of the paper sheets.

FIG. 4 shows an example of such a paper multi-feed detection apparatus using an ultrasonic sensor having the above-described features. The paper multi-feed detection apparatus shown in FIG. 4 has the following structure. A feeding path 42 for feeding a paper sheet 41 two-dimensionally is interposed between a transmitter 44 of an ultrasonic sensor 43 and a receiver 45 of the ultrasonic sensor 43. The transmitter 44 is provided above the feeding path 42, and the receiver 45 is provided below the feeding path 42. The transmitter 44 and the receiver 45 face each other. Transmitting and receiving directions of the transmitter 44 and the receiver 45 are set to be oblique with respect to the feeding path 42.

An ultrasonic wave 46 which is transmitted from the transmitter 44 is directed to a top surface of the paper sheet 41 via an entrance opening 48 for transmitting the ultrasonic wave. The entrance opening 48 is formed in an upper feeding guide plate 47 which covers a top surface of the feeding path 42. The ultrasonic wave 46 directed to the paper sheet 41 is transmitted through the paper sheet 41 and is received by the receiver 45 via an exit opening 50 for transmitting the ultrasonic wave. The exit opening 50 is formed in a lower feeding guide plate 49 which covers a bottom surface of the feeding path 42, and has the same size as that of the entrance opening 48. The attenuation amount (transmission amount) of the ultrasonic wave 46 caused by the transmission through the paper sheet 41 is measured, and thus a control section detects whether one paper sheet 41 is being fed or a plurality of paper sheets are being fed in an overlapped state (see, for example, Patent Document 1).

However, there may be an occasion that when the ultrasonic wave 46 is directed to the paper sheet 41, a part of the ultrasonic wave 46 is reflected by a top face of the paper sheet 46 and the reflected wave is reflected diffusedly in a feeding space 42 a. For example, the paper sheet 41 may be bent in the feeding space 42 a. When being directed to the bent paper sheet 41, the ultrasonic wave 46 is reflected diffusedly. The reflected wave generated as a result of the diffused reflection may occasionally be received by the receiver 45 as a noise component. Such a noise component may deteriorate the capability of the sensor and thus cause erroneous detection of the paper sheet 41.

In an attempt to solve this problem, the technology of Patent Document 1 directs the ultrasonic wave toward the face of the paper sheet obliquely so as to reduce the reflection of the ultrasonic wave by the top face of the paper sheet and also so as to reduce the reflection of the ultrasonic wave by a receiving face of the receiver. However, merely setting the transmitting direction of the ultrasonic wave to be oblique is not sufficient to obtain a sufficient sensor capability.

In addition, devices such as copiers are desired to be reduced in size. Therefore, there is no extra space around the feeding path, which causes many factors generating noise components. FIG. 5 shows another example of a paper multi-feed detection apparatus. This paper multi-feed detection apparatus has a structure in which a feeding path 52 for feeding a paper sheet 51 two-dimensionally is interposed between a transmitter 53 provided above the feeding path 52 and a receiver 56 provided below the feeding path 52. Where there is a component surrounding the feeding path (reflecting object) 55 in or around a transmission section from the transmitter 53 to an upper feeding guide plate 54, the transmission wave reflected by the paper sheet 51 may hit the component surrounding the feeding path 55 to be reflected diffusely and the resultant wave may be received by the receiver 56 as a noise component.

For example, where an ultrasonic sensor and an optical sensor are both provided, a sensor opening 58 for the optical sensor may be formed in the upper feeding guide plate 54 or a lower feeding guide plate 57. In such a case, before the paper sheet 51 which is being fed reaches the sensor opening 58, a transmission wave 59 transmitted through the sensor opening 58 may directly reach the receiver 56 and may be added to the received component. Also, a reflected wave 60 may occasionally reach the receiver 56 from a space in the vicinity of the receiver 56 and act as a noise component. Such a noise component is likely to have an adverse influence on the performance of the paper multi-feed detection apparatus.

According to another known multi-feed detection apparatus, a transmission area and a receiving area of an ultrasonic wave from the transmitter to the receiver are enclosed by a sound-absorbing material to absorb an external noise component and a noise component generated by the reflected wave (see, for example, Patent Document 2).

However, such a structure requires the transmission and receiving areas to be enclosed air-tightly by the sound-absorbing material, and thus decreases the level of designing freedom because the arrangement and the shape of the sound-absorbing material are specified. This structure also has a problem that the ultrasonic sensor itself is costly.

Patent Document 1: Japanese Laid-Open Patent Publication No. 6-72591

Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-82350

In light of the above, the present invention has an object of providing a paper multi-feed detection apparatus and a paper multi-feed detection method capable of properly eliminating the reflected ultrasonic wave, which would otherwise become a noise component, to prevent the detection capability from being deteriorated by the noise component and thus to improve the detection precision.

SUMMARY OF THE INVENTION

The present invention is directed to a paper multi-feed detection apparatus comprising a feeding path covered with one feeding guide plate and another feeding guide plate facing each other while having therebetween a feeding space for feeding a paper sheet two-dimensionally; and a transmitter of an ultrasonic sensor provided on one of two sides facing each other while having the feeding space therebetween, and a receiver of the ultrasonic sensor provided on the other of the two sides. An ultrasonic wave is incident on the feeding space from the transmitter via an entrance opening formed in the one feeding guide plate; the ultrasonic wave output via an exit opening formed in the another feeding guide plate is received by the receiver; paper multi-feed is detected by comparing attenuation information on the ultrasonic wave when the paper sheet passes between the transmitter and the receiver, against a threshold value for multi-feed detection; the entrance opening is formed to be large so as to discharge outside the ultrasonic wave incident thereon and then reflected, without making the reflected wave a noise component; and the exit opening is formed to be smaller than a receiving face area of the receiver for receiving the ultrasonic wave.

In one embodiment of the present invention, the paper multi-feed detection apparatus comprises a feeding path covered with one feeding guide plate and another feeding guide plate facing each other while having therebetween a feeding space for feeding a paper sheet two-dimensionally; and a transmitter of an ultrasonic sensor provided on one of two sides facing each other while having the feeding space therebetween, and a receiver of the ultrasonic sensor provided on the other of the two sides. An ultrasonic wave is incident on the feeding space from the transmitter via an entrance opening formed in the one feeding guide plate; the ultrasonic wave output via an exit opening formed in the another feeding guide plate is received by the receiver; paper multi-feed is detected by comparing attenuation information on the ultrasonic wave when the paper sheet passes between the transmitter and the receiver, against a threshold value for multi-feed detection; an ultrasonic wave transmission area from the transmitter to the entrance opening is in a open state; and an ultrasonic wave receiving area from the exit opening to the receiver is enclosed by a noise shielding wall.

In one embodiment of the present invention, according to a paper multi-feed detection method, where a transmitter and a receiver are provided to face each other while having a feeding path for a paper sheet therebetween, an entrance opening, on which an ultrasonic wave transmitted from the transmitter toward the receiver is incident via a feeding guide plate which covers an ultrasonic wave transmission side of the feeding path, is formed to be large so as to discharge a reflected wave outside; and an exit opening, for outputting the ultrasonic wave via a feeding guide plate which covers an ultrasonic receiving side of the feeding path facing the ultrasonic transmission side, is formed to be smaller than a receiving face area of the receiver.

According to the present invention, a stable transmission capability is guaranteed because a noise component is avoided from being generated at the time of the ultrasonic wave transmission, and a receiving capability can be improved by properly blocking a noise component which is likely to enter the receiver at the time of the ultrasonic wave receiving. Especially, the structure of the present invention does not require any new parts, and can be easily obtained even where there is no ample extra space around the feeding path.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an operation illustration showing a detection state of a paper multi-feed detection apparatus according to Embodiment 1.

FIG. 2 is a block diagram of a control circuit of an ultrasonic sensor which may be incorporated into the paper multi-feed detection apparatus according to Embodiment 1.

FIG. 3 is an operation illustration showing a detection state of a paper multi-feed detection apparatus according to Embodiment 2.

FIG. 4 is an operation illustration showing a detection state of a conventional paper multi-feed detection apparatus.

FIG. 5 is an operation illustration showing a detection state of another conventional paper multi-feed detection apparatus.

DESCRIPTION OF THE REFERENCE NUMERALS

-   11, 31 Paper multi-feed detection apparatus -   13, 33 Feeding path -   14, 15, 34, 35 Feeding guide plate -   16, 36 Ultrasonic sensor -   17, 37 Transmitter -   18, 38 Receiver -   19, 39 Entrance opening -   20, 40 Exit opening -   34 a, Noise shielding wall -   U Ultrasonic wave -   R Reflected wave

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

Hereinafter, one embodiment of the present invention will be described with reference to the figures.

The figures show a paper sheet multi-feed detection apparatus which maybe built in a copier. As shown in FIG. 1, a paper sheet multi-feed detection apparatus 11 includes a main body 12 and a feeding path 13, provided above the main body 12, for feeding a paper sheet P in a horizontal direction two-dimensionally. A top surface of the feeding path 13 is covered with an upper feeding guide plate 14, and a bottom surface of the feeding path 13 is covered with a lower feeding guide plate 15. The upper feeding guide plate 14 and the lower feeding guide plate 15 face each other while having a two-dimensional feeding space 13 a therebetween.

A transmitter 17 of an ultrasonic sensor 16 is provided above the feeding path 13, and a receiver 18 of the ultrasonic sensor 16 is provided below the feeding path 13. The transmitter 17 and the receiver 18 also face each other while having the feeding path 13 therebetween. Transmitting and receiving directions of the ultrasonic sensor 16 are set to be oblique with respect to the feeding path 13, so as to be suitable to transmit and receive an ultrasonic wave U.

An entrance opening 19 is formed in the upper feeding guide plate 14, more specifically at a position where the upper feeding guide plate 14 crosses the transmission wave advancing in the transmitting direction from the transmitter 17. The ultrasonic wave U incident on the feeding space 13 a from the transmitter 17 is reflected by the paper sheet P to become a reflected wave R, which could act as a noise component. The entrance opening 19 is formed to be large so as to discharge the reflected wave R outside the paper multi-feed detection apparatus 11. For example, the entrance opening 19 may have a size sufficiently large to avoid multiple reflections. Herein, “multiple reflections” means that when the ultrasonic wave U is directed to a top surface of the paper sheet P, the reflected wave R directed upward at a certain angle hits the upper feeding guide plate 14 and is reflected again downward. The entrance opening 19 is circular around the center of the transmission area of the ultrasonic wave U from the transmitter 17 and has the largest possible size that does not disturb the feeding capability.

An exit opening 20 is formed in the lower feeding guide plate 15, more specifically at a position where the lower feeding guide plate 15 crosses the receiving wave advancing in the receiving direction toward the receiver 18. The exit opening 20 is formed to be smaller than the size of a receiving face (receiving sensor head) 18 a of the receiver 18 for receiving the ultrasonic wave U, which is output from the feeding space 13 a toward the receiver 18. The exit opening 20 is thus small so as to restrict the area through which the ultrasonic wave U passes to a certain size. This makes it difficult for noise to enter the receiving face 18 a, and the ultrasonic wave U is received by the receiver 18 stably. Preferably, the size of the exit opening 20 is equal to or smaller than the size of the receiving face 18 a of the receiver 18 so as to prevent the noise from entering the receiver 18, or is larger than half of the size of the receiving face 18 a so as to maintain the receiving capability.

FIG. 2 is a block diagram of a control circuit of the ultrasonic sensor 16 which may be incorporated into the paper multi-feed detection apparatus 11. The ultrasonic sensor 16 includes, on the transmission side, an oscillation circuit 21 for generating a signal of a predetermined frequency (for example, 220 kHz) and an amplification circuit 22 for amplifying the signal of the predetermined frequency.

The ultrasonic sensor 16 includes, on the receiving side, a filter/amplification circuit 23 for removing noise and amplifying the received signal, a rectification circuit 24 for detecting the amplified signal, and a determination circuit 25 for comparing the received signal against a reference value for determination.

An electric signal of a predetermined frequency which is output from the oscillation circuit 21 is amplified by the amplification circuit 22 to a predetermined value, is input to the transmitter 17, and is converted into an ultrasonic wave U by a piezoelectric element in the transmitter 17. The resultant ultrasonic wave U is radiated toward the receiver 18 through the paper sheet P which is fed on the feeding path 13. The ultrasonic wave U radiated from the transmitter 17 hits the paper sheet P which is being fed on the feeding path 13, and is partially reflected. The ultrasonic wave U which is transmitted through the paper sheet P is received by the receiver 18, is converted into an electric signal by a piezoelectric element in the receiver 18, and is input to the control circuit on the receiving side. The attenuation degree of the ultrasonic wave U varies depending on whether one paper sheet P is being fed or a plurality of paper sheets P are being fed. The determination circuit 25 compares the transmission amount (attenuation degree) of the ultrasonic wave U against a reference value (threshold value) to detect whether the multi-feed of the paper sheets P is occurring or not. The detection result is transmitted to an upper-stage control section of the device, such as a copier or the like, which incorporates the paper multi-feed detection apparatus 11.

Now, with reference to the operation illustration in FIG. 1, the detection state of the paper multi-feed detection apparatus 11 will be described.

The transmitter 17 of the ultrasonic sensor 16 directs the ultrasonic wave U in the obliquely downward transmitting direction. The ultrasonic wave U thus directed is incident on the feeding space 13 a of the feeding path 13 via the entrance opening 19 formed in the upper feeding guide plate 14. The ultrasonic wave U is directed toward the paper sheet P passing through the feeding space 13 a. At this point, a part of the ultrasonic wave U is reflected by the top surface of the paper sheet P, but goes outside as a reflected wave without hitting the upper feeding guide plate 14 owing to the large entrance opening 19. Thus, the reflected wave does not cause multiple reflections and therefore does not become a noise factor.

Meanwhile, the ultrasonic wave which advances linearly in the transmitting direction and is transmitted through the paper sheet P is received by the receiver 18 while being restricted in the amount by the small exit opening 20 facing the transmitting direction. The exit opening 20 is small so as to restrict the transmission amount of the ultrasonic wave U to a level appropriate for receiving. Therefore, noise is unlikely to enter the receiver 18, and an appropriate amount of the ultrasonic wave U is received by the receiver 18 stably.

Based on the determination result on the received ultrasonic wave U, it is detected on the receiving side whether one paper sheet P is being fed or a plurality of paper sheets P are being fed. When it is determined that one paper sheet P is being fed, normal feeding is confirmed. When it is determined that a plurality of paper sheets P are being fed, it is found that abnormal feeding has occurred and error information is output.

As described above, when the ultrasonic sensor 16 is used for the paper multi-feed detection apparatus 11, the reflected wave which would otherwise act as a noise component can be discharged outside by simply forming the entrance opening 19 for the ultrasonic wave U to be large. By simply forming the exit opening, for the ultrasonic wave U to be received, to be small, the noise can be prevented from entering the receiver 18 and the receiving capability can be improved. The capabilities of the ultrasonic wave can be significantly improved by simply changing the sizes of the entrance opening 19 and the exit opening 20.

Embodiment 2

FIG. 3 shows another paper multi-feed detection apparatus 31. The paper sheet multi-feed detection apparatus 31 includes a main body 32 and a feeding path 33, provided above the main body 32, for feeding a paper sheet P in a horizontal direction two-dimensionally. A top surface of the feeding path 33 is covered with an upper feeding guide plate 34, and a bottom surface of the feeding path 33 is covered with a lower feeding guide plate 35. The upper feeding guide plate 34 and the lower feeding guide plate 35 face each other while having a two-dimensional feeding space 33 a therebetween.

A transmitter 37 of an ultrasonic sensor 36 is provided above the feeding path 33, and a receiver 38 of the ultrasonic sensor 36 is provided below the feeding path 33. The transmitter 37 and the receiver 38 also face each other while having the feeding path 33 therebetween. Transmitting and receiving directions of the ultrasonic sensor 36 are set to be oblique with respect to the feeding path 33, so as to be suitable to transmit and receive an ultrasonic wave U.

An entrance opening 39 is formed in the upper feeding guide plate 34, more specifically at a position where the upper feeding guide plate 34 crosses the transmission wave advancing in the transmitting direction from the transmitter 37. The ultrasonic wave transmission area from the transmitter 37 to the entrance opening 39 is in an open state without being enclosed. Since the ultrasonic wave transmission area is in an open state, when the ultrasonic wave U incident on the feeding space 33 a from the transmitter 37 is reflected by the paper sheet P, the reflected wave R which would otherwise act as a noise component is discharged outside through the open area. Therefore, the multiple reflections in the transmission area can be avoided. An exit opening 40 is formed in the lower feeding guide plate 35, more specifically at apposition where the lower feeding guide plate 35 crosses the receiving wave advancing in the receiving direction toward the receiver 38. The ultrasonic wave receiving area from the exit opening 40 to the receiver 38 is enclosed by a cylindrical noise shielding wall 38 a. This structure prevents external disturbing noise R1 or the reflected wave R from reaching the receiver 38. This makes it difficult for noise to enter the receiver 38, and the ultrasonic wave U is received by the receiver 18 stably.

The elements of the above-described embodiments correspond to elements of the following claims as follows.

The paper multi-feed detection apparatus according to the present invention corresponds to the paper multi-feed detection apparatuses 11 and 31 in the embodiments;

the paper sheet corresponds to the paper sheet P;

one feeding guide plate corresponds to the upper feeding guide plate 14;

another feeding guide plate corresponds to the lower feeding guide plate 15.

The present invention is not limited to the above-described embodiments, and may be applied in various ways based on the technological idea defined by the claims. 

1. A paper multi-feed detection apparatus, comprising: a feeding path covered with one feeding guide plate and another feeding guide plate facing each other while having therebetween a feeding space for feeding a paper sheet two-dimensionally; and a transmitter of an ultrasonic sensor provided on one of two sides facing each other while having the feeding space therebetween, and a receiver of the ultrasonic sensor provided on the other of the two sides; wherein: an ultrasonic wave is incident on the feeding space from the transmitter via an entrance opening formed in the one feeding guide plate; the ultrasonic wave output via an exit opening formed in the another feeding guide plate is received by the receiver; paper multi-feed is detected by comparing attenuation information on the ultrasonic wave when the paper sheet passes between the transmitter and the receiver, against a threshold value for multi-feed detection; the entrance opening is formed to be large so as to discharge outside the ultrasonic wave incident thereon and then reflected, without making the reflected wave a noise component; and the exit opening is formed to be smaller than a receiving face area of the receiver for receiving the ultrasonic wave.
 2. A paper multi-feed detection apparatus, comprising: a feeding path covered with one feeding guide plate and another feeding guide plate facing each other while having therebetween a feeding space for feeding a paper sheet two-dimensionally; and a transmitter of an ultrasonic sensor provided on one of two sides facing each other while having the feeding space therebetween, and a receiver of the ultrasonic sensor provided on the other of the two sides; wherein: an ultrasonic wave is incident on the feeding space from the transmitter via an entrance opening formed in the one feeding guide plate; the ultrasonic wave output via an exit opening formed in the another feeding guide plate is received by the receiver; paper multi-feed is detected by comparing attenuation information on the ultrasonic wave when the paper sheet passes between the transmitter and the receiver, against a threshold value for multi-feed detection; an ultrasonic wave transmission area from the transmitter to the entrance opening is in a open state; and an ultrasonic wave receiving area from the exit opening to the receiver is enclosed by a noise shielding wall.
 3. A paper multi-feed detection method, wherein where a transmitter and a receiver are provided to face each other while having a feeding path for a paper sheet therebetween, an entrance opening, on which an ultrasonic wave transmitted from the transmitter toward the receiver is incident via a feeding guide plate which covers an ultrasonic wave transmission side of the feeding path, is formed to be large so as to discharge a reflected wave outside; and an exit opening, for outputting the ultrasonic wave via a feeding guide plate which covers an ultrasonic receiving side of the feeding path facing the ultrasonic transmission side, is formed to be smaller than a receiving face area of the receiver. 